#include<cstring>
#include<algorithm>
#include<iostream>
using namespace std;
int res;
char start[110], ed[110];
void turn(char &s) {
if (s == '*') s = 'o';
else s = '*';
}
int main() {
cin >> start >> ed;
int n = strlen(start);
for (int i = 0; i < n - 1; i++) {
if (start[i] != ed[i]) {
turn(start[i]), turn(start[i + 1]);
res ++;
}
}
cout << res << endl;
return 0;
}